Generally, an air bag is mounted to a steering wheel or an instrument panel of a vehicle so as to protect a driver or passenger in the event of a collision. When a collision between vehicles occurs, the air bag is inflated so that the passenger does not collide with the panel inside a vehicle or with a windshield, thus reducing the severity of injuries.
Such an air bag includes a cover, an inflater, an air bag module, an impact sensor, and an electronic control module. The cover is mounted to the instrument panel or the steering wheel in such a way that the expanding part of the cover faces a passenger. The operation of the inflater is controlled according to an input operation control signal, so that the inflater generates gas in a collision. The air bag module comprises an air bag cushion which is expanded using the gas generated by the inflater. The impact sensor generates an impact signal when the driving speed is suddenly lowered and the acceleration of gravity reaches a preset value. The electronic control module transmits an electric signal to an igniter, which ignites a gas generating material contained in the inflater in response to the impact signal.
The air bag constructed as described above is operated as follows. That is, when a vehicle is in a collision, impacts are transmitted through a vehicle body, and are detected by the impact sensor, thus determining whether to operate the air bag. When the impacts exceed a preset value, an electric signal is transmitted from the electronic control module to the igniter provided in the inflater, so that the gas generating material is ignited. As such, the gas generated when the gas generating material is ignited is jetted through the inside cylinder and an outside cylinder, so that the air bag cushion is expanded and inflated. The air bag cushion opens the cover, and contacts the body of the driver or passenger. After the air bag cushion contacts the body, the passenger gently rebounds and is returned to his or her original position. At this time, the air bag cushion slowly deflates.
The inflater includes the gas generating material, the inside cylinder, and the outside cylinder. The gas generating material generates gas when the gas generating material is ignited. The inside cylinder has a predetermined space to accommodate the gas generating material and the igniter for igniting the gas generating material in response to an external impact signal, with a plurality of holes formed in the circumference of the inside cylinder. The outside cylinder surrounds the inside cylinder, and has in the circumference thereof a plurality of holes to transmit the gas generated in the inside cylinder to the expanding part, that is, the air bag cushion. The inside cylinder of the inflater is made of wire nets folded several times in order to bear the high temperature and the high pressure of the gas generated due to the ignition of the gas generating material contained in the inflater, in addition to transmitting the gas to the outside cylinder.